协程基础_context系列函数

Posted 2020-09-15 yfceshi

  近期想看看协程，对这个的详细实现不太了解。查了下，协程最常规的做法就是基于makecontext,getcontext,swapcontext这类函数在用户空间切换用户上下文。

所以在这通过样例代码尽量把context相关的函数弄清楚先。

#include <ucontext.h>
#include <stdio.h>
#include <stdlib.h>

static ucontext_t uctx_main, uctx_func1, uctx_func2;

#define handle_error(msg)    do { perror(msg); exit(EXIT_FAILURE); } while (0)

static void
func1(void)
{
   printf("func1: started\n");	//4
   printf("func1: swapcontext(&uctx_func1, &uctx_func2)\n");	//5
   if (swapcontext(&uctx_func1, &uctx_func2) == -1) //切换回func2运行
	   handle_error("swapcontext");
   printf("func1: returning\n");	//7
}

static void
func2(void)
{
   printf("func2: started\n");	//2
   printf("func2: swapcontext(&uctx_func2, &uctx_func1)\n");	//3
   if (swapcontext(&uctx_func2, &uctx_func1) == -1)	//切换到func1运行
	   handle_error("swapcontext");	
   printf("func2: returning\n");	//6
}

int
main(int argc, char *argv[])
{

   //注意在实际中要注意stack大小,否则可能会出现溢出.  
   char func1_stack[16384];
   char func2_stack[16384];

   //获取当前进程/线程上下文信息,存储到uctx_func1中
   if (getcontext(&uctx_func1) == -1)
	   handle_error("getcontext");
	   
   //uc_stack: 分配保存协程数据的堆栈空间
   uctx_func1.uc_stack.ss_sp = func1_stack;	//栈头指针
   uctx_func1.uc_stack.ss_size = sizeof(func1_stack);	//栈大小
   uctx_func1.uc_link = &uctx_main;	//协程兴许的context
   makecontext(&uctx_func1, func1, 0); //依改动得到一个新的centext

   if (getcontext(&uctx_func2) == -1)
	   handle_error("getcontext");
   uctx_func2.uc_stack.ss_sp = func2_stack;
   uctx_func2.uc_stack.ss_size = sizeof(func2_stack);
   /* Successor context is f1(), unless argc > 1 */
   //假设argc有传參数进来,则uc_link置为空.兴许代码将不再运行
   uctx_func2.uc_link = (argc > 1) ? NULL : &uctx_func1;
   makecontext(&uctx_func2, func2, 0);

   printf("main: swapcontext(&uctx_main, &uctx_func2)\n"); //1
   //swapcontext(ucontext_t *oucp, ucontext_t *ucp)
   // 进行上下文切换。将当前上下文保存到oucp中，切换到ucp
   //将当前上下文保存到uctx_main, 并切换到uctx_func2
   if (swapcontext(&uctx_main, &uctx_func2) == -1) 
	   handle_error("swapcontext");

   printf("main: exiting\n"); //8 ： 如argc不为空则这不会运行.
   exit(EXIT_SUCCESS);
}

样例执行结果:

suora:/test # ./co1 5
main: swapcontext(&uctx_main, &uctx_func2)
func2: started
func2: swapcontext(&uctx_func2, &uctx_func1)
func1: started
func1: swapcontext(&uctx_func1, &uctx_func2)
func2: returning
suora:/test # ./co1 
main: swapcontext(&uctx_main, &uctx_func2)
func2: started
func2: swapcontext(&uctx_func2, &uctx_func1)
func1: started
func1: swapcontext(&uctx_func1, &uctx_func2)
func2: returning
func1: returning
main: exiting

从执行结果看，大致弄清这几个函数了，只是我对stack大小还是没弄清楚应当怎么估算，但我把这个样例再实现了下。
弄了个动态分配内存的试了试。

/************************************************* 
Author: xiongchuanliang 
Description: coroutine 

suora:/test # gcc -o co2 co2.c
suora:/test # ./co2
main: swapcontext(&uctx_main, &uctx_func2)
func2: started
func2: swapcontext(&uctx_func2, &uctx_func1)
func1: started
func1: swapcontext(&uctx_func1, &uctx_func2)
func2: returning
func1: returning
main: exiting
suora:/test # ./co2 3 5 
main: swapcontext(&uctx_main, &uctx_func2)
func2: started
func2: swapcontext(&uctx_func2, &uctx_func1)
func1: started
func1: swapcontext(&uctx_func1, &uctx_func2)
func2: returning
suora:/test # 
**************************************************/ 

#include <ucontext.h>
#include <stdio.h>
#include <stdlib.h>

ucontext_t uctx_main, uctx_func1, uctx_func2;

#define handle_error(msg)    do { perror(msg); exit(EXIT_FAILURE); } while (0)
   
#define CONTEXT_STACK (1024*64) // 64kB
typedef void (*context_func)(void);   

void func1(void);
void func2(void);

int ctx_create(ucontext_t 	*ctx,
				context_func func,
				ucontext_t 	*ctx_link,
				void 	*ss_sp,
				size_t 	ss_size);


int main(int argc, char *argv[])
{
   if(ctx_create(&uctx_func1,func1,&uctx_main,
				malloc(CONTEXT_STACK),CONTEXT_STACK) == 1)
		return EXIT_FAILURE;	 	 

		 		
	if(ctx_create(&uctx_func2,func2, 
				(argc > 1) ?
 NULL : &uctx_func1 ,   //&uctx_func1
				malloc(CONTEXT_STACK),CONTEXT_STACK) == 1)
	{
		free( uctx_func1.uc_stack.ss_sp );
		return EXIT_FAILURE;
	}
	 
	printf("main: swapcontext(&uctx_main, &uctx_func2)\n");	
	  
	if (swapcontext(&uctx_main, &uctx_func2) == -1) 
               handle_error("swapcontext");					

	free( uctx_func1.uc_stack.ss_sp );
	free( uctx_func2.uc_stack.ss_sp );
	
   printf("main: exiting\n");
   exit(EXIT_SUCCESS);
}


int ctx_create(ucontext_t 	*ctx,
				context_func func,
				ucontext_t 	*ctx_link,
				void 	*ss_sp,
				size_t 	ss_size)
{
	if(getcontext(ctx) == -1)
	{	 
		handle_error("getcontext");
		return 1;
	} 	   
    ctx->uc_link = ctx_link;
    ctx->uc_stack.ss_sp =  ss_sp; 
    ctx->uc_stack.ss_size = ss_size;
    ctx->uc_stack.ss_flags = 0;
	
	makecontext(ctx, func, 0); 
    return 0;
}


void func1(void)
{
   printf("func1: started\n");
   printf("func1: swapcontext(&uctx_func1, &uctx_func2)\n");
   if (swapcontext(&uctx_func1, &uctx_func2) == -1)
	   handle_error("swapcontext");
   printf("func1: returning\n");
}

void func2(void)
{
   printf("func2: started\n");
   printf("func2: swapcontext(&uctx_func2, &uctx_func1)\n");
   if (swapcontext(&uctx_func2, &uctx_func1) == -1)
	   handle_error("swapcontext");
   printf("func2: returning\n");
}

今天先弄到这.


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